1. Field of the Invention
The invention relates to a light plunger piston for internal combustion engines.
It is the object of the invention to improve the noise characteristics of such a piston during engine operation, with the lowest possible weight and smallest possible dimensions. At the same time, the piston is supposed to produce the least possible friction losses during engine operation.
2. Description of the Prior Art
A piston is known from WO 88/08078. The solution path striven for there, however, will not be taken by the present invention.
The solution with the piston according to WO 88/08078 consists of allowing the piston to run at an angle relative to its piston head in operating states at which the piston has not yet reached the temperature which prevails in its rated performance operation. For this purpose, the piston shaft or skirt is provided with a corresponding contour, which changes with an increasing operating temperature of the piston, in that the piston head is aligned parallel to the engine cylinder axis during rated performance operation of the piston. The slanted position of the piston head at lower temperatures, which exists during partial load operation of the engine, is aimed at so that the piston head can be held as far away as possible from the cylinder wall on that side on which it tends to hit against the cylinder wall as the result of its tilt movement. The risk of an impact against the cylinder wall particularly exists on the counterpressure side or minor thrust face, and for this reason, the piston head is angled in such a way that there is a greater distance between the top land and the cylinder wall on the counterpressure side or minor thrust face than on the pressure side or major thrust face.
The slit below the bottom piston ring groove is provided on the minor thrust face in this known piston, in order to interrupt the heat flow from the hot piston head to the skirt area below it, on that side. Such an interruption of the heat flow is necessary so that the skirt undergoes as little expansion radially towards the outside as possible, due to heat, at its upper end. A control strip additionally applied to the upper end of the skirt on the minor thrust face in this known piston, which has a lower coefficient of expansion as compared with the skirt material, also serves to prevent such an excessive radial expansion. With the combined measure of the slit and the heat-expansion-damping control strip, it is possible with this piston to create a skirt contour change in the direction of the rod swing plane (plane in which the piston axis extends and stands perpendicular to the piston pin axis) on the minor thrust face, which moves the piston head into a position parallel to the cylinder axis with an increasing piston temperature.
The result which can be achieved with this embodiment is to be further improved with a piston embodiment according to the invention.